Through-tubing nonretrievable bridge plug

ABSTRACT

Several concentric sections of tubing are telescoped over each other with each section except the innermost being slotted longitudinally and with the slots of one section being circumferentially offset from the slots of adjacent sections. The inner most section includes a central passageway extending along its entire axial length with a bypass valve disposed at the lower end of the passage. When the innermost section is pulled axially upwardly with respect to the outer sections, the slotted portions are forced radially outwardly to engage and lock to the surrounding well structure. The locking means retains the radial expansion and the central passageway conducts well fluids through the assembly. The valve may thereafter be set to completely close the passageway.

United States Patent [72] lnventor Arthur L. Owen Houston, Tex. [21] Appl. No. 764,438 [22] Filed Oct. 2, 1968 [45]. Patented Feb. 9, 1971 [73] Assignee Electric Wireline Specialties, Inc.

Alice, Tex. a corporation of Texas [54] THROUGH-TUBING NONRETRIEVABLE BRIDGE PLUG 22 Claims, 6 Drawing Figs.

[521 US. Cl 166/182, 166/191,166/196,166/213,166/241 [51] Int. Cl ..E21b33/134 [50] Field of Search 166/117, 118,123,126,127,l33,179,188,196, 206, 207, 213, 216, 217, 241;277/116.8

[56] References Cited UNITED STATES PATENTS 1,804,818 5/1931 Spang 166/196X 2,082,113 6/1937 Layne et al. 166/118X 2,701,615 2/1955 Riordan et a1. 166/188X 9/1955 Bell et al 166/117 2.944,608 7/1960 Rush 166/241 3,282,347 1 H1966 Chenoweth 166/196 3,318,385 5/1967 Conrad 166/212 1 3,378,078 4/1968 Current 166/126X 3,438,438 4/1969 Conrad 166/212X Primary Examiner-Jan A. Calvert Attorney-Carlos A. Torres ABSTRACT: Several concentric sections of tubing are telescoped over each other with each section except the innermost being slotted longitudinally and with the slots of one section being circumferentially offset from the slots of adjacent sections. The innermost section includes a central passage way extending along its entire axial length with a bypass valve disposed at the lower end of the passage. When the innermost section is pulled axially upwardly with respect to the outer sections, the slotted portions are forced radially outwardly to engage and lock to the surrounding well structure. The locking means retains the radial expansion andthe central passageway conducts well fluids through the assembly. The valve may thereafter be set to completely close the passageway.

INVILN'lY/R.

Arthur L. Owen 234557 Ill/fi PATENIEH FEB 9197:

ATTORNEY THROUGH-TUBING NONRETRIEVABLE BRIDGE PLUG BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of well treatment and operation. More specifically, the present invention relates to a through-tubing, nonretrievable bridge plug which is designed to be set securely within a well conduit during the subsurface treatment and operation of oil and gas wells.

In oil and gas operations, it is sometimes necessary to form a stationary obstruction at a particular subsurface location within the well structure. Such obstructions are often employed to seal off undesirable fluids in the well or to permit production from lower zones in the formation. Often, the obstruction may be required within the well bore casing itself or it may be required for smaller diameter tubing disposed within the well casing. Where such obstructions are required, a suitable tool is secured to a supporting structure and lowered into the tubing string or well casing to the desired subsurface location. When the desired subsurface location is reached, the tool body is set or anchored in the well conduit and released from the supporting structure used to lower it into position. The setting action usually is performed by expanding the components of the tool body radially causing the tool to engage and frictionally lock against the surrounding well structure. When properly positioned and set, the tool may function to completely seal off the well conduit or it may merely act as a support for holding cement or other material which may be deposited over the tool. In some special purpose applications, the tool may carry valving mechanisms or other equipment for treating or controlling fluid or gas flow in the well conduit.

2. Description of the Prior Art Bridge plugs commonly employed in oil and gas wells usually are provided with means for expanding the plug body radially and locking it in its expanded condition against the internal tubular surface of the well conduit. Often, the body of the plug includes an expansible elastomeric packer disposed between upper and lower metal slips or teeth. When such plugs are set, the teeth engage the well conduit and function to effect a mechanical friction lock while the elastomeric packer is foreshortened axially to provide a seal with the surrounding well conduit. Two plugs or packers exemplary of such downhole devices are illustrated in US. Pat. No. 2,737,242 issued to Baker and US. Pat. No. 3,343,607 issued to Current. Plugs of the type illustrated in the Baker and Current patents often require a relatively large number of interrelated and closely fitting components and as a consequence are often relatively expensive to produce and assemble and are subject to malfunctioning. Moreover, the radial dimensions of this type plug are often fairly large and as a result they are subject to being stuck or prematurely set in the well conduit.

In certain well operations, such as cementing, an elastomeric plug may sometimes be employed as a bridging means. The plug is compressed into the well conduit and driven down to its subsurface location by pressurizing the well conduit above the plug. Because of the absence of rigid structure in such plugs, they are often incapable of supporting weights over a certain maximum value and are consequently unsuitable for applications requiring cement deposits in excess of the limiting weight value. Moreover, the final positioning of the resilient plug is not as controllable as it is with other type plugs and if the plug lodges at an undesirable subsurface location, difficult resetting or retrieving measures may be required.

Still another bridge plug commonly employed in cementing operations employs a sealing disc of canvas secured above a metal locking body. The plug is set by a cement dump which releases several spring-loaded locking dogs formed in the metal locking body which act to lock the bridge plug against the surrounding well conduit to prevent downward movement of the plug. Cement is then dropped over the canvas disc carried at the top of the plug to form the desired seal. This latter plug is, however, also subject to displacement and uncertainty in setting which may be caused by slippage of the dogs against the tubing wall. This danger is partially attributable to the use of spring loading for the setting force rather than the more positive method of applying a strong external force and mechanically locking the components in place. As with the previously noted bridge plugs, the radial dimensions of the latter plug are also relatively large and the dangers of sticking or premature setting remain present.

US. Pat. No. 3,282,347 to Chenoweth illustrates another type of bridge plug employed in cementing and similar operations. The Chenoweth bridge plug employs a central mandrel extending through a longitudinally slotted tubular body. When the central mandrel is pulled upwardly relative to the surrounding tubular body, the slotted portions of the body collapse radially outwardly and engage and lock with the surrounding well conduit. A series of Belleville washers are simul taneously compressed to maintain the lateral forces exerted by the plug. Continued pulling of the central mandrel releases the setting mechanism from the plug and releases a number of pellets and rods which fall over the expanded portion of the plug body to cover the spaces formed by enlargement of each of the slots. Cement or other material is then deposited above the plug in the customary manner. In a second version of the Chenoweth plug, a basket is opened above the slotted portion of the plug when the latter is set to receive the cement and prevent it from falling through the enlarged slots of the plug body.

For most effective setting of the Chenoweth plug. the dimensions of the plug body and its operative components must be proportioned to the dimensions of the well conduit. The plug body is shaped and cut to expand in a specific manner and to a predetermined degree and as a result for most effective setting, the plug and well conduit dimensions must conform to each other within a relatively narrow range. If the internal dimensions of the well conduit are too large or too small, the plug body must be expanded beyond or below its optimum design specifications which may produce an inferior set of the plug in the conduit.

Although the radial dimensions of the Chenoweth plug may be relatively small compared with the dimensions of the well conduit, the plug is relatively expensive to manufacture because of the requirement for special shaping and cutting of the slotted portion of the plug body. It is further complicated in its construction by the requirement for Belleville washers for maintaining the radial forces exerted by the plug and additional means such as filler pellets and rods or an expansible basket for preventing the cement or other material from falling through the slots in the expanded tool body.

Another problem associated with certain of the previously described bridging tools, including the Chenoweth bridge plug, is caused by the flowing of well fluids or gasses through the unhardened cement deposited over the plug. When this occurs, the high pressure fluids or gas below the plug may bubble up or flow through the unset cement or where the formation is taking fluid, the fluid may wash away all or a portion of the unset cement as it flows past the plug.

BRIEF DESCRIPTION OF THE INVENTION The bridge plug of the present invention includes seven tubing sections of increasing diameter with the smaller diameter sections being telescoped or carried within the next larger diameter sections. Each of the six outer sections is provided with two expansible areas comprising two axially spaced sets of eight longitudinally extending slots which are formed about the circumference of the section. The slots in each set are of the same length and are equally spaced circumferentially about the tubing with the slots in each tubing section being circumferentially offset midway between the slots of the next adjacent tubing sections.

The innermost tubing section or mandrel is unslotted and longer than the slotted sections and extends axially above and below such sections. The upper axial end of the mandrel is provided with means for securing the bridge plug to a setting mechanism and a second means for locking the bridge plug in its set position. The lower axial end of the innermost section is provided with an enlarged valve housing which acts as a fixed base for the slotted tubing sections and also houses a bypass valve mechanism.

The bridge plug is set in the well tubing by pulling the innermost tubing section upwardly with respect to the overlying slotted sections. This movement foreshortens the outer sections of tubing and forces the ribs in the expansible slotted areas of the tubing to bow radially outwardly and engage the surrounding well conduit. Continued pulling eventually severs a shear pin which frees the setting mechanism from the bridge plug and the plug is then retained in its expanded position by the locking means provided at the upper end of the mandrel.

When thus set, the concentric tubing sections cooperate to increase the structural strength of the bridge plug and exert great lateral pressure against the well conductor to firmly anchor the plug in place.

Cement or other bridging material may then be deposited over the bridge plug by any conventional means. The wet cernent or other material so deposited is prevented from falling past the set bridge plug in that the circumferential offsetting of slots in adjacent sections causes the slots of one tubing section to :e partially or completely covered by the solid portions or ribs of adjacent tubing sections, thereby obviating the need for additional sealing means. If a pressure differential exists across the cemented area, the higher pressure gas or fluid above or below the plug is free to flow through the bypass valve and through the central passage way in the mandrel. Gas or fluid flow through the wet cement itself is thereby avoided and the cement may dry to a solid, uniform mass.

After the completion of the cementing operation described above, more cement may be deposited over the cured cement and the well conduit may thereafter be pressurized above the cement barrier to close the bypass valve in the mandrel and prevent upward fluid or gas flow, or the rate of fluid flow past the valve components may be increased to close the valve against downward flow. The latter cement deposite completely seals over the well conduit and after it has cured, the fluid or gas pressure applied at the well head may be terminated.

The bridge plug of the present invention is relatively inexpensive to fabricate and assemble in that no milling or molding steps are required and only a simple cutting procedure is needed for forming the slots in the tubing sections. Moreover, the amount of permissible radial expansion of the ribs in the slotted areas is relatively great and is not dependent upon complex shaping or design. As a result, one size of the bridge plug of the present invention may be employed in a greater range of well conduit sizes than is possible with certain of the prior art devices. The radial dimensions of the bridge plug of the present invention are also relatively small when the plug is unset which permits unobstructed travel through the well conduit and when set, the inherent strength and resiliency of the plug body obviates the requirement for additional means for maintaining a firm engagement with the well conduit.

Other advances and features of the bridge plug of the present invention will be apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevation of the bridge plug of the present invention;

FIG. 2 is a partial elevation, in section, of the bridge plug of the present invention;

FIG. 3 is a cross sectional view of the bridge plug of the present invention taken along the line 3-3 of FIG. 1;

FIG. 4 is an elevation of the bridge plug of the present invention as it appears when set in a well conduit;

FIG. 5 is a cross-sectional view of the bridge plug of the present invention taken along its expansible portion; and

FIG. 6 is an enlarged sectional view illustrating the locking means of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1 of the drawings, the bridge plug of the present invention is indicated generally at 10 and includes an outermost tubing section 11 of steel or other suitable material having longitudinally extending slots 11a and 11h formed at longitudinally spaced positions along its length. As best illustrated in FIGS. 2 and 3, similar tubing sections 12, I3, l4, l5 and 16 of respectively decreasing diameter are telescoped within the outer tubing section 11. The outer diameter of each of the sections 12-16 preferably conforms closely to the inner diameter of its overlying tubing section to provide a relatively tight assembly. Each of the tubing sections 12, 13, 14, 15 and 16 is also provided with equal length, axially extending slots 12a, 13a, 14a, 15a and respectively which have the same length as the slots 11a and are developed on their respective tubing sections at the same axial position along the plug body 10. A second similar set of equal length slots 12b, 13b, 14b, 15b, and 16b is formed in the tubing sections 12, 13, 14, 15, and 16 respectively with such second set of slots also being longitudinally developed and coextensive with the slots 1 lb along the same axial position of the body 10. It should be observed that the slots 12b, 14b and 16b are not visible in the various views of the drawing, however, their position and construction will be implicit from the illustrated structure.

As best illustrated in FIGS. 2 and 3 of the drawings, the tubing sections are disposed in such a manner that the slots of one section are centered between the slots of the next adjacent inner and outer tubing sections. The circumferential relationship of the slots in each of the sections is fixed by means of a pin P which extends laterally through the tubing sections 11- --I6 at midlength and prevents relative motion between the sections. As will be seen hereinafter, setting of the bridge plug 10 increases the lateral dimensions of the slots formed in each of the tubing sections and the metal ribs between the slots of one tubing section may either completely bridge the slots of the overlying section, or if sufficient slot spread occurs, the ribs of several tubing sections will cooperate to bridge a single slot.

With reference to FIGS. 1, 2 and 3, a central tubular section or mandrel 17 is disposed axially through the center of the bridge plug 10 and extends beyond the upper and lower axial end surfaces of the tubing sections 11-16. A locking assembly indicated generally at 18 encircles the upper portion of the mandrel 17 and an attachment assembly indicated generally at 19 is secured to the upper axial end of the mandrel 17. The lower axial end of the mandrel 17 carries a bypass valve indicated generally at 20.

As best illustrated in FIG. 2, the fitting attachment 19 includes an internally threaded collar 19a which is threadedly engaged with external threads formed about the upper axial end of the mandrel 17. A shear pin 19b extends through diametrically disposed lateral bores formed in the collar 190, the mandrel 17 and a shaft S. As will be hereinafter explained in greater detail, the shaft S is one component of a mechanism which may be employed to set the bridge plug 10. A setting sleeve C which is also a part of the setting mechanism extends over the shaft S and adapter fitting l9 and removably engages the upper axial end surface of the locking mechanism 18.

The setting of the bridge plug 10 requires some means for holding the locking assembly 18 stationary relative to an upward movement of the mandrel 17. This motion may be performed by one of several well known devices or by the apparatus described in U. S. Pat application Ser. No. 764,763 filed on Oct. 3,1968, now US. Pat. No. 3,503,444 entitled Electric Setting Mechanism for Subsurface Well Tools" and invented by the instant inventor. The setting mechanism partially illustrated in FIG. 2 is designed to maintain the sleeve C stationary while drawing the shaft S in an upward direction. During such movement of the setting mechanism, the locking mechanism 18 is held stationary by its engagement with the setting sleeve C while the mandrel 17 is drawn upwardly by its mechanical linkage with the shaft 8.

With reference to the lower end of the bridge plug 10, it may be observed that the valve 20 includes a housing 20a in which is loosely carried a spherical closure member or ball 20!). The lower portion of the housing 20a also carries a resilient coil spring member 20c which prevents the ball 20b from seating against an internal seating surface 20d as fluid moves downwardly through the valve 20. Such flow through the valve 20 occurs when the formation is taking fluid supplied from the well head. ln other applications where thewell pressure is greater below the tool than above, the spring 20c may be omitted. Also carried internally of the housing 200 is a retaining ring 20e which prevents the ball 20b from leaving the confines of the valve 20. It should be observed that although not specifically illustrated, the retaining ring 20c is provided with suitable means to permit gas or fluid flow in an upward direction even when engaged with the ball 20b. The upper end of the valve housing 20a is internally threaded and engages external threads formed about the lower portion of the mandrel 17 to securely unite the two components while the lower axial end of the housing 20 is provided with an axial bore 20h. A resilient O-ring 20f of rubber or other suitable material is disposed between the valve housing 20a and the mandrel 17 to provide a secure, leakproof engagement between the two mating components. The upper end of the valve housing 20a also includes a tapered surface 20g which acts as a sloping bearing surface for the lower axial end surfaces of the tubing sections 11-16 during the setting procedure. The lower end of the locking assembly 18 is also provided with a tapered surface 18a and is designed tobear against the upper axial end surfaces of the tubing sections 11-16 during the setting procedure. The purpose and function of the tapered surfaces 20g and 18a will hereinafter be described in greater detail.

The structure and operation of the locking assembly 18 may best be described by reference to FIGS. 2 and 6. The assembly 18 includes a circular collar or pusher 18b which engages a second backup collar 180 having a lower tapered surface 18a, previously described, and an internally tapered surface 18d. A radially slotted tapering ring 18e having internal teeth 18f is slidably carried on the tapered surface 18d. During the setting procedure, the mandrel 17 is pulled upwardly through the backup collar 18c and pusher 18b and the lockring 18a is also raised upwardly by the engagement of the lockring teeth 18f with teeth 17a formed on the external surface of the mandrel 17. As may be observed from the drawings, each of the teeth 17a and the teeth 18f includes a sloped or taperedsurface which intersects a lateral surface and when the upper axial end surface of the lockring 18e engages the pusher 18b further upward movement is precluded and the tapered surface of the mandrel teeth 17a bear against the tapered surface of the ring teeth 18f causing the lockring to expand outwardly. It should be observed that the outward expansion of the lockring 18e is permitted by radially slotting the ring at one point along its circumference as is well known. The ring is preferably constructed of a relatively strong, resilient material such as steel to support the large forces exerted upon it and to contract it to its original circular shape when the radially directed expanding forces are relieved.

When the plug tool breaks free from the setting mechanism during the setting procedure, the mandrel 17 moves downwardly through the locking assembly 18 and the lateral faces of the mandrel teeth 17a engage and bear against the lateral faces of the lockring teeth 18f which forces the lockring 18c downwardly against the tapered surface 18d of the backup collar 18c. Continued downward movement against the tapered surface 18d closes the lockring l8e about the mandrel l7 and locks the teeth 17a and 18f tightly together to prevent any further downward movement of the mandrel 17. From the foregoing description, it is apparent that the locking assembly 18 permits the upward movement of the mandrel through the assembly which is required for expanding the body of the plug 10 while preventing any downward movement therethrough to maintain the expanded condition of the plug.

ln setting the bridge plug 10 of the present invention, the plug 10 and setting mechanism are initially lowered to the desired subsurface location within the well conduit and the setting mechanism is then activated causing the tapered valve housing surface 20g to close toward the tapered surface on the backup collar 180. As this movement continues, the tubing sections ll--Il6 are foreshortened causing the metal ribs in the expansible slotted areas to move radially outwardly until the well conduit is engaged. Continued closing together of the surfaces 20g and 18a causes the metal ribs to flatten out against the well conduit to provide a greater area of surface contact and a more secure anchoring. The amount of expansion of the tubing sections may be governed by the strength of the shear pin 1% and when a predetermined amount of stress has been exerted by the upward motion of the setting mechanism, the shear pin 19!) disrupts and releases the center mandrel 17. At this point, the locking; assembly 18 is activated as previously described by the initial downward movement of the mandrel 17 and the bridge plug is then securely locked in its expanded position. The setting mechanism and support line may thereafter be removed from the well and the cement or other material may be deposited over the plug 10.

When the initial deposit of cement over the bridge plug has been made, the annular space between the body of the plug and the well conduit is completely closed over. Thereafter, any high pressure gas or fluid present above or below the cement is forced to flow through the center of the plug by way of axial bore 20h, valve housing 20a and mandrel 17. It will be apparent that the setting shaft S is completely removed when the bridge plug 10 is set and presents no obstruction to the internal passage within the mandrel 17. The provision of a central passageway in the bridge plug 10 permits the cement surrounding the tool to cure to a solid, uniform mass devoid of any air pockets or channels. Once the initial cement deposit has set up to the desired degree, a second cement deposit is made immediately above the first. The rate of fluid flow through the tool and into the formation is then increased to the extent required to depress the spring 200 and seat the ball 20b against the surface 20d. This pressure is maintained until the second cement deposit has adequately set up and is then released. The second cementing operation thereby completely closes over the flow path through the cement plug and bridge plug 10 and completely seals over the well bore. Where the well pressure is greatest below the bridge plug 10, the spring 200 is omitted and the ball 20b may "be seated by simply sealing over the well head, or if necessary by applying pressure at the well head until the second deposit of cement has cured.

It should be observed at this point that in those applications where there is no differential pressure across the length of the bridge plug 10, the second cementing operation is not required. In the latter situation, the cement initially deposited over the plug is free to enter and seal the central passageway in the tool body thereby effecting complete closure of the well conduit.

FIG. 4 of the drawings illustrates the bridge plug 10 of the present invention as it appears when set within a well conduit W. Greater surface. contact of the ribs with the internal surface of the well conduit W could, of course, be achieved by further foreshortening of the tubing sections. When the tubing sections are foreshortened beyond a certain degree, dependent upon the diameter of the tubing, the number of slots in each section and their length, the ribs from several of the interior tubing sections will expand over the space created by the slots in an outer tubing section. This is illustrated in FIG. 4 of the drawings and is attributable in part to the fact that the inner tubing sections are foreshortened more than the outer sections because of the taper formed on the bearing surfaces 18a and 20g.

As best illustrated in FIG. 5 of drawings, which is a cross section taken along one of the slotted portions of the bridge plug 10, foreshortening of the tubing sections to a lesser degree, permits the ribs of an inner tubing section to completely span the slot of the next adjacent overlying section. It will be apparent that in all of the illustrated degrees of expansion. each underlying tubing section supports the overly ing section and all of the sections cooperate to form a struc' turally strong assembly with almost complete sealing of the well conduit.

While the bridge plug of the present invention has been described as including two axially spaced expansible areas along the tubing sections. it may in practice have one or a multitude of such areas. The use of at least two axially spaced slotted areas is preferable to the extent that greater axial stability and greater surface contact with the well conduit are provided. Similarly, while the preferred form of the present invention has been illustrated as including six concentric slotted tubing sections, and one unslotted central section, a greater or smaller number of such slotted sections may be employed. In like manner, the number of slots formed in each expansible area of the tubing section may be varied as required. If desired, the metal ribs in the slotted areas may also be provided with a series of lateral grooves or other means, including abrasives or other suitable material for increasing the frictional engagement with the well conduit.

The foregoing disclosure and description of the'invention is illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made within the scope of the a; pended claims without departing from the spirit of the invention.

lclaim:

ll. A bridge plug for forming a fixed subsurface obstruction in an oil or gas well conduit comprising:

a. a longitudinally developed central mandrel having first and second axially spaced ends;

b. a plurality of telescoped, longitudinally developed tubular members carried over said mandrel;

c. said tubular members having at least one expansible area including a plurality of longitudinally extending, circumferentially spaced slots formed on each of said tubular members;

d. setting means for longitudinally foreshortening saidtubular members to force said expandable area laterally outwardly; and

e. 'lockingmeans for retaining said tubular members in a foreshortened condition.

2. The bridgeplug as defined in claim 1 wherein said central mandrel includes a central passageway extending between said first and second ends and further including valve means carried at one end of said mandrel for controlling fluid or gas flow'through said central passageway.

3. The bridge plug as defined in claim 2 further including a plurality of said expansible areas formed at longitudinally spaced positions along said tubular members.

' 4. The bridge'plug as'defined in claim 3 wherein the slots of one tubularmember are circumferentially offset from the slots of adjacent tubular members in'the same expansible area.

5. Thebridge plug as defined in claim 4 wherein the slots of each tubular member are'substantially equally circumferentially spaced about said tubular-member and are of substantially the same length.

6. The bridge plug as defined in claim 5 wherein saidsetting means includes a first convexly tapered bearing surface formed on said locking means and a second, oppositely directed convexly tapered bearing surface formed on said valve means.

7. The bridge plug as defined in claim 4 including:

a. pin means for maintaining the circumferential relationship of said plurality of tubular members;

b. a first convex bearing surface formed on said valve 'means for engaging oneaxial end of said plurality of tubular members;

0. a'second oppositely directed convex bearing surface formed on said locking-means for bearing against the other axial end of said pluralityof tubular members; and

d. releasing means carried on said center mandrel for releasing said mandrel from the equipment used toanchor said bridge plug in the conduit.

8. The bridge plug as defined in claim 7 wherein said valve means includes a ball and seat for closing said valve means against fluid or gas flow through said passageway in said center mandrel 9 The bridge plug as defined in claim '8 wherein said locking means includesv a. a plurality of circumferentially developed external grooves formed on said central mandrel: and

b. a slotted ring having a plurality of internal, circumferentially developed grooves for locking with said grooves on said mandrel.

10. The bridge plug as defined in claim 7wherein saidvalve means includes a movable ball closuremember disposed over a resilient spring element'and a fixed apertured valve seat for receiving'said ball and closing said passagewayin said'mandrel against fluid or gas flow.

11. The bridge plugas defined in claim 2 wherein the slots of one tubular member are circumferentially offset from the slots of adjacent tubular members in the same expansible area 12. The bridge plug as defined in-claim 2 wherein said setting means includes a first convexlytapered bearing surface formed on said locking means and a second, oppositely directed convexly taperedbearing surface formed on said valve means.

13. The bridge plug asdefined in claim 2 wherein:

a. said locking means is carried adjacent said first end of said mandrel;

b. said valve means is carried on said second end of said mandrel; and

c. said tubular members are disposed between saidlocking means and said valve means.

14. The bridge plug as defined in claim 13 wherein said setting means includes:

a. a first convex bearing surface formed on said valve means for engaging one axialend of said plurality of tubular members; and

b. a second oppositely directed convex bearingsurface formed on said locking means for bearing against the other axial end ofsaidplurality of tubular members.

15. The bridge'plug as defined in claim 2 further including a plurality of said expansible areas formed at longitudinally spaced positions along said tubular member.

16. The bridge plug as defined in claim 15 wherein:

a. said locking means is carried adjacent said first end of said mandrel;

b. said valve means is carried on said second'endof said mandrel;

c. said tubular member is disposed'between said locking means and said valve means; and

(1. said setting means includes a first convexly taperedbearing surface formed on said locking=means and a second, oppositely directed convexly tapered bearing surface formed on said valve means.

17. The bridge plug as defined in claim 1 including a'plurality of said expansibleareas formed at longitudinally spaced positions alongs'aid tubular members.

18. The bridge'plug as defined in claim- 17 wherein theslots of one tubular-memberare circumferentially offset from the slots of adjacent tubular members in the same expansible area.

19. The bridge plug as defined in claim 18 whereinthe slots of each tubular member are substantially equally circumferentially spaced about said tubular'me'r'nberand are'of substantially the same length.

20. The bridge plug as defined'in claim 1 wherein the slots of one tubular member are circumferentially offset'from the slots of adjacent tubular members in the-same expansible area.

21. The bridgeplug as defined'in claim 1 wherein the slots of each tubular member are substantially equally circumferentially spaced about said tubular member and are of-s'ubstantially the same length.

22. The bridge plug as defined in claim 1 wherein said setting means includes at'leastone tapered bearing surface for engaging said-tubular members. 

1. A bridge plug for forming a fixed subsurface obstruction in an oil or gas well conduit comprising: a. a longitudinally developed central mandrel having first and second axially spaced ends; b. a plurality of telescoped, longitudinally developed tubular members carried over said mandrel; c. said tubular members having at least one expansible area including a plurality of longitudinally extending, circumferentially spaced slots formed on each of said tubular members; d. setting means for longitudinally foreshortening said tubular members to force said expandable area laterally outwardly; and e. locking means for retaining said tubular members in a foreshortened condition.
 2. The bridge plug as defined in claim 1 wherein said central mandrel includes a central passageway extending between said first and second ends and further including valve means carried at one end of said mandrel for controlling fluid or gas flow through said central passageway.
 3. The bridge plug as defined in claim 2 further including a plurality of said expansible areas formed at longitudinally spaced positions along said tubular members.
 4. The bridge plug as defined in claim 3 wherein the slots of one tubular member are circumferentially offset from the slots of adjacent tubular members in the same expansible area.
 5. The bridge plug as defined in claim 4 wherein the slots of each tubular member are substantially equally circumferentially spaced about said tubular member and are of substantially the same length.
 6. The bridge plug as defined in claim 5 wherein said setting means includes a first convexly tapered bearing surface formed on said locking means and a second, oppositely directed convexly tapered bearing surface formed on said valve means.
 7. The bridge plug as defined in claim 4 including: a. pin means for maintaining the circumferential relationship of said plurality of tubular members; b. a first convex bearing surface formed on said valve means for engaging one axial end of said plurality of tubular members; c. a second oppositely directed convex bearing surface formed on said locking means for bearing against the other axial end of said plurality of tubular members; and d. releasing means carried on said center mandrel for releasing said mandrel from the equipment used to anchor said bridge plug in the conduit.
 8. The bridge plug as defined in claim 7 wherein said valve means includes a ball and seat for closing said valve means against fluid or gas flow through said passageway in said center mandrel.
 9. The bridge plug as defined in claim 8 wherein said locking means includes: a. a plurality of circumferentially developed external grooves formed on said central mandrel; and b. a slotted ring having a plurality of internal, circumfErentially developed grooves for locking with said grooves on said mandrel.
 10. The bridge plug as defined in claim 7 wherein said valve means includes a movable ball closure member disposed over a resilient spring element and a fixed apertured valve seat for receiving said ball and closing said passageway in said mandrel against fluid or gas flow.
 11. The bridge plug as defined in claim 2 wherein the slots of one tubular member are circumferentially offset from the slots of adjacent tubular members in the same expansible area
 12. The bridge plug as defined in claim 2 wherein said setting means includes a first convexly tapered bearing surface formed on said locking means and a second, oppositely directed convexly tapered bearing surface formed on said valve means.
 13. The bridge plug as defined in claim 2 wherein: a. said locking means is carried adjacent said first end of said mandrel; b. said valve means is carried on said second end of said mandrel; and c. said tubular members are disposed between said locking means and said valve means.
 14. The bridge plug as defined in claim 13 wherein said setting means includes: a. a first convex bearing surface formed on said valve means for engaging one axial end of said plurality of tubular members; and b. a second oppositely directed convex bearing surface formed on said locking means for bearing against the other axial end of said plurality of tubular members.
 15. The bridge plug as defined in claim 2 further including a plurality of said expansible areas formed at longitudinally spaced positions along said tubular member.
 16. The bridge plug as defined in claim 15 wherein: a. said locking means is carried adjacent said first end of said mandrel; b. said valve means is carried on said second end of said mandrel; c. said tubular member is disposed between said locking means and said valve means; and d. said setting means includes a first convexly tapered bearing surface formed on said locking means and a second, oppositely directed convexly tapered bearing surface formed on said valve means.
 17. The bridge plug as defined in claim 1 including a plurality of said expansible areas formed at longitudinally spaced positions along said tubular members.
 18. The bridge plug as defined in claim 17 wherein the slots of one tubular member are circumferentially offset from the slots of adjacent tubular members in the same expansible area.
 19. The bridge plug as defined in claim 18 wherein the slots of each tubular member are substantially equally circumferentially spaced about said tubular member and are of substantially the same length.
 20. The bridge plug as defined in claim 1 wherein the slots of one tubular member are circumferentially offset from the slots of adjacent tubular members in the same expansible area.
 21. The bridge plug as defined in claim 1 wherein the slots of each tubular member are substantially equally circumferentially spaced about said tubular member and are of substantially the same length.
 22. The bridge plug as defined in claim 1 wherein said setting means includes at least one tapered bearing surface for engaging said tubular members. 